I'd agree it's definately easier to introduce a younger cat as they seem less of a threat. Neutered boys seem to have a great bond in all the situations I've seen. We introduced a kitten to our 18 month old boy earlier in the year and although it took a little while to get used to each other, they are now SO close and are always together. Whatever cat you decide on, and it always depends on the individual cat's personality- there are no clear cut answers, you must make sure you do the introductions very carefully and patiently. If you get to that stage there are lots of people on here who can give great advice on that.